Change font face/size of the top GTKWindow?

I'm trying to use .NET Core GTK. For WinForms, we can select the form, and then click the Font property to change the font face or size within the Form designer. If we change the top form's font, it is applied to all the child controls on the form.

I wanted to do similar thing in Glade, but I cannot find a "Font" GUI in any of the attribute tabs.

Is this possible with GTK#?
If so, can it be done within Glade?
If the answer to 2 is no, can it be done in the code?

Solution

Yes this is possible in both GTK and Glade, although some code will be required to change all the forms font.

In GTK you will be using the GtkFontChooserWidget. This should let you choose between fonts.

In Glade, when you are using the attributes tab you are able to change font size with the Scale attribute. I haven't yet figured out how to change the actual font through those attributes yet. Thankfully there is a workaround. Instead of using Attributes, use Markup. Markup works just fine for both font size and font style.

Markup Example

<span font='36' face='Georgia'>Markup</span>

Assuming you are using a GtkComboBoxText to list possible fonts and button for selecting, you would just need a handler that would go through each of the labels and change the font to the designated one.

def when_visible(window):
"""
This is where per-window initialization takes place.
Values to be displayed are populated into their widgets.
"""
global FONT_FACE
name = Gtk.Buildable.get_name(window) # Window currently on

if 'font_select_screen' = name:
    font = BUILDER.get_object('fontEntryCombo')
    FONT_FACE = font.get_active_text()
elif 'random_screen' = name:
    label1_text = "<span font='36' face='{}'>Label</span>".format(FONT_FACE)
    label1 = BUILDER.get_object('label1')
    label1.set_markup(label1_text)